Currently, most printed materials, for example, books, greeting cards, and lottery tickets, are fully printed before their purchase. With devices such as greeting cards which are meant to convey a message, one must choose from a limited number of messages available; the correct or desired message is not always available for purchase. In addition, the message conveyed is not one chosen or composed by the sender.
Children's books are used as tools for teaching reading and writing. These books typically have simple sentences with illustrations to convey the meaning of the text. In books which are meant to teach both reading and writing, it is known to leave blanks in the text which the child can fill in. The blank areas are typically filled in in such a way that the word written thereon may be erased to allow the books to be reused. The parent or teacher may then instruct the child by reviewing the text after the child has filled in the blanks. In this way, the child is taught to comprehend the text at the same time she or he is taught to read and write. However, in this learning process it is necessary to have an adult review the material to correct any mistakes. As a result, the child cannot learn without adult supervision.